I only use Mann air filters. You won't see any performance boost with an oiled filter and it will kill your MAS over time. Even still I cleaned mine with some hope of seeing some MPG gain. Its recommended to clean it every time you change your air filter.

A word of advice: if you decide to clean your MAS: you don't have to take the air filter housing out. I know a lot of people do but you should have plenty of room. No need in working any harder than you must.